Radio repeater



Patented Aug. 13, 1946 RADIO REPEATER J. Ernest Smith, Brooklyn, N. Y., assgnor to Radio Corporation of America, a corporation of Delaware Application February 12, 1942, Serial No. 430,527

er tubes -available at the present time. To overcome this difficulty, the ultra high frequency signal is heterodyned to a lower frequency band, amplified and heterodyned back to an ultra high frequency band for retransmission. Further, the retransmitted band normally does not coincide with the received frequency band but is difierentially spaced therefrom to avoid feedback between the transmitting and receiving antennas and their associated circuits. While the present heterodyning practice permits satisfactory amplification at ultra high frequencies, it introduces, at the same time, the necessity for frequency monitoring of the retransmitted signal since its frequency is a function of the heterodyning oscillator frequency. Moreover, if the relay system incorporates antennas having band Widths sufficient for the simultaneous transmission of a video channel and an adjacent sound or cue channel, it is possible for cross-talk to result due to drift of the heterodyning frequencies at one of the repeaters.

An object of the present invention is to overcome the foregoing difficulties and disadvantages.

A further object of the present invention is to improve the frequency stability of radio relay equipment.

Another object of the present vinvention is the provision of a radio relay station which may be conveniently controlled and supervised from the terminal stations of a relay system.

A further object of the present invention is the provision of a relay system which will not require frequency monitoring at each of the intermediate repeater stations.

Still a further object of the present invention is the provision of a system of amplifying ultrahigh frequency radio waves wherein the output signal from the amplifier means is determined substantially only by the frequency of the incoming waves.

The foregoing objects and others, which may appear from the following detailed description,

30 Claims. (Cl. Z50-15) are obtained in accordance with the principles of the present invention by providing a crystal controlled oscillator and another oscillator, mixing the output of said oscillators or modulating the output of one of the oscillators, either in amplitude or wavelength, by the other of the oscillators and separating the sum and difference frequencies thus obtained. One of these frequencies is mixed with an incoming band of frequencies to obtain a signal at a comparatively low intermediate frequency Which may be conveniently amplified without adversely affecting the width of the band of the frequencies. The amplified band of frequencies is then mixed with the other of the sum and difference frequencies to convert the band to a position in the radio frequency spectrum near that of the incoming band of frequencies and, also, thus dropping out the effect of any frequency drift in the local oscillator. The converted band of frequencies is then transmitted to the Succeeding amplifiers in the relay system.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which:

Figure 1 illustrates the frequency distribution, in a portion of the radio frequency spectrum, of various frequencies used in an embodiment of the invention; While Figure 2 is a diagram in conventional block formation of an embodiment of the invention;

Figure 3 is a curve illustrating the operation of a portion of Figure 2; and

Figure 4 illustrates a modification of the embodiment of Figure 2, and a different order of application of the operations of the invention.

Reference will now be had to the drawing, Figure 1 shows the frequency spectrum arrangement wherein the incoming frequency fs is heterodyned with a local frequency (fc-fk) giving the low intermediate frequency band (fs-fc-l-fk) lwhich may be amplified with-out difliculty. The amplified signal is then heterodyned with another local frequency (fc-l-fk), thus resulting in the frequency (JS-i-2fk) which is to be retransmitted. The frequencies fc and fk from which the sum and difference frequencies are derived are locally produced by oscillation generators, that for frequency fk being crystal controlled. It will be noted that the outgoing frequency (fs-l-Zfk) is independent of the oscillator frequency fc.

The frequency ,fk may conveniently be of the order of 10 megacycles and is, therefore, preferably derived from a crystal oscillator. Its drift,

3 l therefore, compared to the outgoing carrier frequency of the order of 500 megacycles is negligible. n

In Figure 2 is shown an embodiment of the invention for performing the operations outlined above. Frequency fk is generated by crystal oscillator I and applied to balanced modulator I2 in a push-pull relationship. Another frequency fe generated by oscillator I4 vis applied to balanced modulator I2 in push-push relationship.Y This is a well known carrier suppression system of modulation and therefore needs no further description.

The output frequencies from balanced modulator I2 consist substantiallyof two side" bands only, namely, (fc-fk) and (fc-Hr). The frequency (fc-fk) is applied to converter I6 and there heterodyned with an incoming signal` is arriving from a preceding station by way of-receiving antenna RA, giving an intermediate frequency (fs-fe-i-fk). This frequency may be amplified in a conventional amplifier I8 toV any desired extent. After` ainplication the intermediate frequency signal is Vheterodyned with the component (fc-HJC) in converter 20 thus producing the output frequency (fs-l-Zfr). The output frequency is applied to transmitting antenna TA for retransmission to succeeding relay stations'. The antennas RA and TA Lare preferably of the directive type with their zonesof maximum response directed away from each other and toward relay stations.

It should be understood that the frequency components shown in Figures'l and 2 and specifically mentioned are those which are essential to the operation of the system. Other modulation products would be present but selective circuits in the system may be provided to discriminate against them. Therefore, in order to reduce the number of other modulation products a filter 3D is provided in the channel between converter 2i) and modulator I2 and a filter 32 is provided between converter I5 and modulator I2. These filters assure that only a single frequency as indicated is fed tofeach converter. Then the output of converter I 6 may be arranged to pass only the desired difference frequency fs-fc-l-fk while discriminating, for example, against the sum frequency Js-l-fc-fk. Likewise, the output of converter 2l) may be arranged to pass only the sum frequency fs-l-Zjk discriminating, for example, against the difference frequency JS-Zfcv. In order to illustrate the stability of the outgoing signal (fel-21%), suppose a frequency drift of 5 kilocyclesis allowed crystal oscillator IQ. Theoutgoing signal then has a maximum drift rof l0 kilocycles in 50 megacycles or .002 percentA which, for all practical purposes, is negligible. Obviously, the method described above is equally applicable to an amplitude or to a frequency modulationA system. Y Y

The system asso far described insures that Athe retransmitted frequency band will not-drift'. Y,lt does not, however, maintain the frequency band to be amplified, that is, the frequency (fs-fe-l-fe), constant since this frequency is a function of jc. Due to the difficulty of obtaining wide enough pass bands at low frequencies to vobviate the effect of this drift, according to a further aspect of the present invention, automatic frequency control of oscillator I4 may be provided. Side band clipping in amplifier I8 is thus prevented since the position 0f band (s-.fc-I-Jk) is maintained constant. This may be accomplished by supplying discriminator unit 22, Aresponsive to the AzeroL A shift in either direction will result in a positive or negative resultant output potential. This direct resultant output potential is arranged to be applied as a variable bias to oscillator I4 whereby the frequency fc is controlled in such sense that the output frequencies of modulator I2 are shifted in the desired direction.

In vFigure 4 is shown a modification of the embodiment of Figure 2 wherein the balanced modulator arrangement I2 of Figure 2 is not used. In this figure the incoming frequency is shown as (fs-l-Zfk) the output frequency of the embodiment of Figure 2. The discriminatory characteristics of lter networks 30 and 32 are relied upon to Aselect the first lower and upper side bands (fc-fk) and (fc-Hr) resulting from a mixing of frequencies fc and fk, in modulator 24, while rejecting the frequency je and components of higher order. Since rather severe selectivity isl required of Afilter networks Si? and 32 to discriminate against the frequency fc while passing frequencies (fc-fk) and (gfe-l-fk) for straight mixing or amplitude modulation, the crystal oscillator output fk may be arranged to frequency modulate in modulator 24 the frequency fe generated by oscillator I4. The modulation index may be adjusted to emphasize the rst of the side bands with respect to the frequency fe and higher order components. For example, if a modulation index of about 2.4 is used, the amplitude of frequency fc is reduced to zero and at the same time the maximum fundamental or first order side band amplitudes are obtained. The channel carrying frequencies (fc-I-fk) and (fe-fk) may include an amplitude hunting transducer device if desired. While I have used a modulation index of 2.4 in order to illustrate the selective property of this type of modulation, it is to be clearly understood that my invention is not limited to that value, since under some circumstances` a modulation index of about 1.8 may be preferable. A modulation index of this order gives aA maximum ratio of fundamental to carrier and fundamental to second order side band amplitudes. The amplified intermediate frequency is fs-fc-I-jk, the same as in the previous example. It is then heterodyned with the other side band frequency (fcfr) andthe Vupper beat frequency, which becomes fs, selected for retransmission. The outgoing frequencies of the Vrepeaters using alternate orders of application of the side band frequencies thus are alternately js and (fel-2jr) throughout the system.

While I have particularly described and illustratedseveral modiiicationsof the present invention, Vit should be distinctly understood that my invention is not limited thereto butmay be varied within the scope o f the appended claims.

l. In a radio relay system, a stationincluding receiving and transmitting antennae, a low-frequency oscillator of high frequency stability, an-

other oscillator, modulator means for so combining the output of said oscillators that sum and difference frequencies are generated, a first converter means for mixing one of said frequencies with incoming high frequency energy from said receiving antenna for obtaining a low interme` diate frequency, means for amplifying said intermediate frequency, a second converter means for mixing the other of said sum and difference frequencies With said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation.

2. In a radio system, a source of high frequency energy, a low frequency oscillator of high frequency stability, another oscillator, modulator means for so combining the output of said oscillators that sum and difference frequencies are generated, a rst converter means for mixing one of said sum and difference frequencies with said first mentioned high frequency energy for obtaining a low intermediate frequency, means for amplifying said intermediate frequency, a second converter means for mixing the other of said sum and difference frequencies with said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said source.

3. Ina radio relay system, a station including receiving and transmitting antennae, a loW frequency oscillator of high frequency stability, another oscillator, modulator means for so combining the output of said oscillators that sum and difference frequencies are generated, a first converter means for mixing said difference frequency with incoming high frequency energy from said receiving antenna for obtaining a W intermediate frequency, means for amplifying said intermediate frequency, a second converter means for mixing said sum frequency with said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation. s

4. In a radio system, input and output circuits for high frequency energy, a low frequency oscillator of high frequency stability, another oscillator, modulator means for so combining the output of said oscillators that sum and difference frequencies are generated, a first converter means for mixing said difference frequencies with high frequency energy from said input circuit for obtaining a low intermediate frequency, means for amplifying said intermediate frequency, a second converter means for mixing said sum frequency with said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of the energy at said input circuit and means for applying said output energy to said output circuit.

5. In a radio relay system, a station including receiving and transmitting antennae, a low frequency oscillator of high frequency stability, another oscillator, modulator means for so combining the output of said oscillators that side band frequencies are generated, a first Converter means for mixing one of said side band frequencies with incoming high frequency energy from said receiving antenna for obtaining a 10W intermediate frequency, means for amplifying said intermediate frequecy, a second converter means for mixing another of said side band frequencies With said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation.

6. In a radio system, a station including receiving and transmitting antennas, a 10W frequency oscillator of high frequency stability, another oscillator, means for so applying the output of said low frequency oscillator to said other oscillator that the Wavelength of Ythe output is modulated thereby, a first converter means for mixing one output frequency with incoming high frequency energy from said receiving antenna for obtaining a low intermediate frequency, means for amplifying said intermediate frequency, a second converter means for mixing another of said output frequencies With said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation.

'7. In a radio relay system, a station including receiving and transmitting antennae, a low frequency oscillator of high frequency stability, another oscillator, modulator means fo-r so combining the output of said oscillators that sum and difference frequencies are generated, a first converter means for mixing one of said frequencies With incoming high frequency energy from said receiving antenna for obtaining a 10W intermediate frequency, means for amplifying said intermediate frequency, a second Converter means for mixing the other of said sum and difference frequencies With said amplied intermediate frequency to obtain output energy at a high frequency adjacent the frequency of Said incoming energy and means for applying said output energy to said transmitting antenna for radiation, means equally responsive in opposite senses to said sum and difference frequencies for obtaining a control potential and means for applying said potential to control the frequency of said other oscillator.

18. In a radio relay system, a station including receiving and transmitting antennae, a low frequency oscillator of high frequency stability, another oscillator, means for so modulating the frequency of said other oscillator by said low frequency oscillator that sum and difference frequencies are generated, a first converter means for mixing one of said frequencies With incoming high frequency energy from said receiving antenna for obtaining a low intermediate frequency, means for amplifying said intermediate frequency, a second converter means for mixing the other of said sum and difference frequencies with said amplified intermediate frequency t-o obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation.

9. In a radi-o relay system, a station including receiving and transmitting antennae, a low frequency oscillator of high frequency stability, anotherV oscillator, means for so modulating the fre. quency of said other oscillator by said low frequency oscillator that sum and difference frequencies are generated, a rst converter means for mixing one of said frequencies with incoming high frequency energy from said receiving antenna for obtaining a low intermediate frequency, means for amplifying said intermediate frequency, a second converter means for mixing the other of said sum and difference frequencies With said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for in opposite senses to said sum and difference frel quencies for obtaining a control potential and means for applying said potential to control the frequency of said other oscillator.

10. In a radio relay system, a station including receiving and transmitting antennae, a. low frequency oscillator of high frequency stability; anotherV oscillator, modulator means for so combining the output of said oscillators that sum and difference frequencies are generated, a first con-- verter means for mixing said difference frequency with incoming high frequency energy from said receiving antenna for obtaining a low intermediate frequency, means for amplifying said intermediate frequency, a second converter means for mixing said sum frequency with said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation, means equally responsive in opposite senses to said sum and difference frequenciesmfor obtaining a control potential and means for applying said potential to control the frequency of said other oscillator.

11. In a radio relay system, a station including receiving and transmitting antennas. Ya low frequency oscillator of high frequency stability, another oscillator, means for frequencyA modulating said other oscillator by said low frequency oscillator, thelmodulation index being such that the sum and difference frequencies predominate in the output. a first converter means for mixing said difference frequency with incoming high frequency energy from said receiving antenna for obtaining a low intermediate frequency, means for amplifyingsaid intermediate frequency, a second converter meansfor mixing said sum frequency with said amplified Y intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation.

12. In a radio relay system, astation including receiving and transmitting antennas, a low frequency oscillator of high frequency stability, an-

other oscillator. means for frequency modulating Y the output, a rst converter means for mixing said difference frequency with incoming high freqency energy from said receiving antenna for obtaining a low intermediate frequency, means for amplifying-said intermediate frequency, a second converter means for mixing said sum frequency with said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying saidv output energy to said transmitting antenna for radiation, means equallyY responsive in opposite senses to said sum and difference frequencies for obtaining a control potential and means for applying said potential to control the frequency of said other oscillator.

13. In a radioY relay system, a station including receiving and transmitting antennas, a low frequency oscillator of high frequency stability, another oscillator, modulator means for so combining the output of said oscillators that sum and difference frequencies are generated, a first converter means for mixing said sum frequency with incoming high frequency energy from said receiving antenna for obtaining a low intermediate frequency, meansfor amplifying said intermediate frequency, a second converter means for mixing said difference frequency with said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation, means equally responsive in opposite senses to said sum and difference frequencies for obtaining a control potential and means for applying said potential to control the frequency of said other oscillator.

14. In a radio relay system, a station including receiving and transmitting antennas, a'low frequency oscillator of high frequency stability, another oscillator, means for modulating the Wavelength of the output of said other oscillatorby fied intermediate frequency to obtain output energy'at a high frequency adjacent the frequency of said incoming energy and means for applying said output energy to said transmitting antenna for radiation.

15. In aV radio relay system, a station including receiving and transmitting antennas, a low frequency oscillator of high frequency stability, an-

other oscillator, means for modulating the Wavelength of the output of said other oscillator by said low frequency oscillator, filter means for separating the sum frequency and the difference frequency from the output of said modulator, a first converter means for mixing one of said frequencies with incoming high frequency energy from said receiving antenna for obtaining a low intermediate frequency, means for amplifying said intermediate frequency, a second converter means for mixing the other of said sum and differenceV frequencies `With said amplified intermediate frequency to obtain output energy at a high frequency adjacent the frequency of said incoming energy and means for applying said output energyV to said transmitting antenna for radiation.

16. A radio relay system including a plurality of stations as set forth in claim l, alternate ones of said stations utilizing said difference frequency in said first converter and said sum frequency in said second converter, the other stations of said system having the order of application of said sum and difference frequencies reversed.

17. A radio relay system including a plurality of stations as set forth in claim 8, alternate ones of said stations utilizing said difference frequency in said first converter and said sum frequencyl in said second converter, the other stations of said system having the order of application of said sum and difference frequencies reversed.

18. A radio relay system including a plurality of stations as set forth in claim 9, alternate onesV 19. In a radio system, a source of high fre- ,f quency energy, a low frequency oscillatorof high f.

frequency stability, another oscillator, modulator means for so combining the output of said oscillators that sum and difference frequencies are generated, a converter means for mixing one of said sum and difference frequencies With said first mentioned high frequency energy for obtaining a low intermediate frequency and means for obtaining a control potential from said low intermediate frequency and means for utilizing said control potential to control the frequency of said other oscillator.

20. In a radio system, a low frequency oscillator of high frequency stability, another oscillator, means for so applying the output of said low frequency oscillator to said other oscillator that the Wavelength of the outputU is modulated thereby, converter means for mixing one output frequency from said modulating means with other high frequency energy to obtain a low intermediate frequency and utilization means for said low intermediate frequency.

21. In a radio system, a station including a receiving antenna, a low frequency oscillator of high frequency stability, another oscillator, means for so modulating the frequency of said other oscillator of said low frequency oscillator that sum and difference frequencies are generated. converter means for mixingr one of said frequencies with incomingr high frequency energy from said receiving antenna for obtaining a low intermediate frequency, utilization means for said intermediate frequency and means equally responsive in opposite senses to said sum and difference frequencies for obtaining a control potential and means for applying said potential to control the frequency of said other oscillator.

22. In a radio system, a station including a receiving antenna, a low frequency oscillator of high frequency stability, another oscillator, means for modulating the Wavelength of the output of said other oscillator by said low frequency oscillator, converter means for mixing the rst upper sideband frequencies of the output of said modulator means with incoming high frequency energy from said reeceiving antenna for obtaining a low intermediate frequency, and means for amplifying said intermediate frequency.

23. 'I'he method of Wave conversion Which includes generating a relatively W frequency local wave. generating a local carrier wave, frequency modulating the'carrier wave With the local Wave to such a degree that the carrier has substantially zero value in the Waves resulting from the modulation process in order to facilitate filtering of side bands on either side of the carrier, filtering a side band frequency resulting from the modulation process. heterodyning a wave to be converted with the filtered side band, and utilizing a beat wave resulting from the heterodyning process.

24. The method of wave conversion which includes generating a relatively 10W frequency local Wave, generating another local Wave. frequency modulating said other local Wave With the first mentioned local Wave to such a degree that the said other local wave has substantially zero value in the Waves resulting from the modulation process in order to facilitate selection of one of the remaining modulation products, selecting a side band frequency resulting from the modulation process, heterodyning a wave to be converted with the selected side band, and utilizing a beat Wave resulting from the heterodyning process.

25. The method of wave conversion which includes generating a relatively low frequency local wave, generating a local carrier wave, frequency modulating the carrier Wave with the local Wave to such a degree that the carrier has substantially zero Value in the waves resulting from the modulation process in order to facilitate filtering of side bands on either side of the carrier, filtering a side band frequency resulting from the modulation process, heterodyning the `wave to be converted with the filtered side band, selecting a beat wave resulting from the heterodyning process, heterodyning the beat to a high frequency, and utilizing the resultant high frequency Wave.

26. The method of Wave conversion which includes generating a local Wave, generating a local carrier Wave, frequency modulating the carrier with the local Wave to such a degree that the carrier is reduced substantially to zero in the Waves resulting from the modulation process in order to facilitate filtering of side bands apart from the carrier, filtering a side band frequency Wave lying to one side of the carrier frequency, heterodyning a Wave to be converted with the filtered side band frequency wave, amplifying a beat Wave resulting from the heterodyning process, and heterodyning the amplified beat with another side band frequency filtered from the modulated waves.

27. The method of converting modulated waves of a given mean frequency to modulated waves of another mean frequency which includes generating a local relatively high frequency carrier wave, generating a relatively low frequency Wave, producing sum and difference frequencies with the locally generated Waves, successively heteroclyning waves derived from the modulated Waves of given mean frequency with the said sum and difference waves, and utilizing a beat Wave derived from the last heterodyning process.

28. The method of converting modulated Waves of given mean frequency to Waves of another mean frequency Which includes generating a local carrier wave, generating a local constant frequency modulating Wave, carrier suppression modulating the carrier with the 10W frequency 4 modulatingr Wave, ltering the side bands resulting from the modulation, heterodyning the modulated Waves of mean frequency with one of the side bands to produce a relatively low, readily amplifiable modulated intermediate frequency wave, amplifying the relatively 10W, readily ampliiiable intermediate frequency wave, and heterodyning the amplified intermediate frequency wave against the other filtered side band to produce the modulated waves of the desired mean frequency.

29. The method as defined in the claim 28 Which includes the step of utilizing a portion of the carrier suppression modulated waves to control the frequency of one of the locally generated Waves.

30. The method of wave conversion which includes locally generating a pair of Waves of different frequency, producing sum and difference frequency Waves from the locally generated Waves, utilizing a portion of the sum and difference Waves to frequency control the frequency of one of the locally generated Waves, and successively heterodyning waves derived from waves of one mean frequency with said sum and difference frequency Waves to produce a Wave of different mean frequency.

J. ERNEST SMITH. 

